Synergistic Co-doping and Te-defects engineering in NiTe₂ single-crystals for enhanced hydrogen evolution in acidic...

Transition metal dichalcogenides (TMDs) are promising hydrogen evolution reaction (HER) catalysts due to their layered structures and tunable electronic properties. However, NiTe₂ suffers from suboptimal hydrogen adsorption energy (ΔG_H*) and low active site density. Here, we propose a synergistic strategy involving Co doping and Te vacancy engineering to optimize HER performance in both acidic and alkaline electrolytes of Ni_1-xCo_xTe₂ single crystals. Co²⁺ doping induces linear contraction of the a-axis lattice parameter, reducing charge transfer resistance by 80%. The synchronously formed Te vacancies significantly increase active site density, as evidenced by a 31% enhancement in double-layer capacitance. Optimized Ni_0.6Co_0.4Te₂ achieves near-ideal ΔG_H* (-0.0345 eV), delivering ultralow overpotentials of 419 mV (acidic) and 362 mV (alkaline) at 10 mA cm^-2-17% and 26% lower than pristine NiTe₂ respectively-with >80 h stability. This work establishes a scalable strategy for designing bifunctional electrocatalysts operable in acidic and alkaline media.